The invention relates to carriage motor control for printers. More particularly, it is directed to a controller which appropriately determines a deceleration start position of the carriage motor in accordance with characteristics of the carriage motor so that the carriage stops at a predetermined position.
Many printers are designed to print during acceleration and deceleration of the carriage motor to improve their throughput. To eliminate wasteful travel of the carriage, as well as to improve throughput and downsize the printer, it is necessary to accurately measure acceleration and deceleration distances of the carriage. Particularly, the distance required for deceleration is an important factor in determining the minimum distance that is necessary and sufficient for the carriage to travel after the carriage has started decelerating at an optimal position.
A step motor or a dc motor is usually used as the carriage motor. The deceleration distance is constant for the step motor, whereas it varies for the dc motor since dc motor characteristics change due to changes in temperature and load. Therefore, printers using a dc motor as a carriage motor start decelerating the carriage motor at a safe position that is sufficiently close to the print end position, taking into account such deceleration distance variations. In other words, the deceleration start position is determined on the basis of a sufficiently short distance that has been determined as a deceleration distance in advance.
However, the conventional method of determining the deceleration start position is not satisfactory from the viewpoint of throughput improvement and downsizing. The reason is that if the motor winding resistance is increased due to an increase in motor temperature, the current flowing into the motor decreases, which then reduces the braking torque. This makes the actual deceleration distance longer than the estimated deceleration distance, thus causing the carriage to travel a longer distance upon completion of printing.
Similar problems that are attributable to motor characteristic variations will be addressed not only in regard to deceleration control but also in regard to various other aspects of carriage motor control.